1. Field of the Invention
The present invention relates to an SOI (Silicon On Insulator) substrate having a single crystal silicon layer on one surface of a support substrate, an element substrate having the SOI substrate, a semiconductor device having the SOI substrate, an electro-optical apparatus having the element substrate, an electronic equipment, a method of manufacturing the SOI substrate, a method of manufacturing the element substrate, and a method of manufacturing the electro-optical apparatus.
2. Description of the Related Art
At first, a semiconductor technique for forming a single crystal silicon thin film on an insulation substrate and, by using the single crystal silicon thin film, forming a semiconductor device is referred to as an “SOI technique”. This technique is widely used since it has the merits of a higher speed of an element, a lower consumptive electric power, a higher integration and the like.
As one of the SOI techniques, there is a technique for manufacturing the SOI substrate by laminating the single crystal silicon substrate. The method of manufacturing the SOI substrate and the structure thereof are briefly explained here with reference to FIG. 28(a) and FIG. 28(b).
At first, as shown in FIG. 28(a), a single crystal silicon substrate 1003, whose surface is oxidized to be a silicon oxide film 1002 at a lamination side thereof, is laminated on a surface of a support substrate 1001 by using a hydrogen coupling force. Then, their lamination strength is increased by a heat treatment. After that, as shown in FIG. 28(b), the thickness of the single crystal silicon substrate 1003 is reduced by grinding, polishing, etching or the like to thereby form a single crystal silicon layer 1004. Accordingly, the SOI substrate is manufactured in which the silicon oxide film 1002 and the single crystal silicon thin film 1004 are laminated in this order on the surface of the support substrate 1001.
According to the above-mentioned method of manufacturing the SOI substrate, the single crystal silicon thin film 1004 that is excellent in the crystal property can be formed as the thickness of the single crystal silicon substrate 1003 is reduced. Thus, it is possible to produce a device having a high performance.
The SOI substrate manufactured by such a laminating method is used to produce various devices, similarly to a bulk semiconductor substrate (i.e., a semiconductor integrated circuit). However, as the feature different from the bulk substrate, the SOI substrate has a feature that the substrate made of various materials can be used as the support substrate.
That is, the typical silicon substrate can be naturally used as the support substrate. Moreover, it is possible to use a transparent quartz substrate (having an optically transparent property), a glass substrate or the like. For this reason, for example, by forming the single crystal silicon thin film on the substrate having the optically transparent property, a transistor element, such as MOSFET or the like for driving a liquid crystal of a high performance can be formed by using the single crystal silicon thin film which is excellent in the crystal property, even in an apparatus requiring the optically transparent property, for example, a transparent type of a liquid crystal display device.
However, if the SOI substrate is manufactured by using the quartz substrate or the glass substrate as the support substrate, and the transistor element is formed on the surface thereof, impurities contained in the support substrate may be permeated through the silicon oxide film and diffused into the side of the transistor element. This results in the fear of the deterioration in the element property.
Also, there may be a case that the impurities such as Na+, K+, Cl− and the like are absorbed from the atmosphere onto the lamination plane, when the support substrate and the single crystal silicon substrate are laminated together in the process for manufacturing the SOI substrate, irrespectively of the kind of the support substrate. In this case, in the manufactured SOI substrate, the above-mentioned impurities are sandwiched between the support substrate and the silicon oxide film.
If the SOI substrate having the above-mentioned structure is used to form the transistor element on the surface, the impurities sandwiched between the support substrate and the silicon oxide film are permeated through the silicon oxide film and diffused into the transistor element side. This results in the fear of the deterioration in the element property.
When the support substrate and the single crystal silicon substrate are laminated together, a dust-proof filter or the like may be used in order to prevent the atmospheric impurities from being absorbed onto the support substrate. Actually, even if the dust-proof filter is used, it is difficult or impossible to perfectly prevent the atmospheric impurities from being absorbed onto the lamination surface.
Secondly, for example, in a case of an electro-optical apparatus of a TFT active matrix driving type, if an input light is irradiated onto a channel region of a thin film transistor (hereafter, which is referred to as a TFT (Thin Film Transistor) as the occasion demands) for a pixel switching operation, which is disposed at each pixel, an optical excitation causes an optical leak current to be generated, which changes the TFT property. In particular, in a case of an electro-optical apparatus for a light valve in a projector, since the strength of the input light is high, it is important to perform a light shield for the input light with respect to the channel region of the TFT as well as the peripheral region thereof. So, the light shield is performed with respect to the channel region as well as the peripheral region thereof by using a light shield film, which is originally designed to define an open region of each pixel and is disposed on an opposite substrate, and/or by using a data line, which is passed over the TFT on the TFT array substrate and is made of a metallic film such as Al (Aluminum) or the like.
In particular, there may be a case that the light shield film made of, for example, metal of high melting point is disposed even at a lower side of the TFT on the TFT array substrate. By disposing the light shield film at the lower side of the TFT in this manner, it is possible to prevent (i) a rear reflection light from the side of the TFT array substrate and (ii) a return light, such as a projection light which has passed through a prism or the like from another electro-optical apparatus in case of combining a plurality of electro-optical apparatuses through prisms and the like to thereby configure one optical system, from being inputted to the TFT of the electro-optical apparatus.
However, according to the research of the inventor of this application, the light shield film, which is formed at the lower side of the TFT and is made of the metal of the high melting point and the like, exhibits the tendency of the increase in aging oxidation during the manufacture of a product or the usage after the completion of the product. Then, if such oxidation is increased in the light shield film, it is confirmed that a light transmission rate is increased depending on the degree of the oxidation. This results in a problem that the increase in the oxidation causes the original function of the light shield film to be not sufficiently provided. For example, if a normal pressure oxidation at an oxygen content of 15% and a water content of 85% is performed with respect to the TFT array substrate in which the light shield film made of such high melting point metal is formed at the lower side of the TFT, the example is confirmed in which the light shield film having a film thickness of about 200 nm is perfectly oxidized even if it is covered by the protective insulation film made of silicon oxide film having a film thickness of about 800 nm.
Moreover, according to the research of the inventor of this application, the above-mentioned arrangement of the light shield film made of the high melting point metal and the like at the lower side of the channel region of the semiconductor layer constituting the TFT results in a problem of the contamination caused by the light shield film in this semiconductor layer (e.g., the contamination caused by the diffusion of the impurities and the like). That is, as compared with the case in which such a light shield film is not disposed, the example of the increase in the impurities permeated into the semiconductor layer is also confirmed, which results in a problem of the deterioration in the transistor property of the TFT.